// Copyright (c) 2011 Google, Inc. // // Permission is hereby granted, free of charge, to any person obtaining a copy // of this software and associated documentation files (the "Software"), to deal // in the Software without restriction, including without limitation the rights // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell // copies of the Software, and to permit persons to whom the Software is // furnished to do so, subject to the following conditions: // // The above copyright notice and this permission notice shall be included in // all copies or substantial portions of the Software. // // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN // THE SOFTWARE. // // CityHash, by Geoff Pike and Jyrki Alakuijala // // This file provides a few functions for hashing strings. On x86-64 // hardware in 2011, CityHash64() is faster than other high-quality // hash functions, such as Murmur. This is largely due to higher // instruction-level parallelism. CityHash64() and CityHash128() also perform // well on hash-quality tests. // // CityHash128() is optimized for relatively long strings and returns // a 128-bit hash. For strings more than about 2000 bytes it can be // faster than CityHash64(). // // Functions in the CityHash family are not suitable for cryptography. // // WARNING: This code has not been tested on big-endian platforms! // It is known to work well on little-endian platforms that have a small penalty // for unaligned reads, such as current Intel and AMD moderate-to-high-end CPUs. // // By the way, for some hash functions, given strings a and b, the hash // of a+b is easily derived from the hashes of a and b. This property // doesn't hold for any hash functions in this file. #ifndef CITY_HASH_H_ #define CITY_HASH_H_ #include // for size_t. #include #include /** This is a version of CityHash that predates v1.0.3 algorithm change. * Why we need exactly this version? * Although hash values of CityHash are not recommended for storing persistently anywhere, * it has already been used this way in ClickHouse: * - for calculation of checksums of compressed chunks and for data parts; * - this version of CityHash is exposed in cityHash64 function in ClickHouse SQL language; * - and already used by many users for data ordering, sampling and sharding. */ namespace CityHash_v1_0_2 { typedef uint8_t uint8; typedef uint32_t uint32; typedef uint64_t uint64; /// Represent an unsigned integer of 128 bits as it's used in CityHash. /// Originally CityHash used `std::pair` instead of this struct, /// however the members `first` and `second` could be easily confused so they were renamed to `low64` and `high64`: /// `first` -> `low64`, `second` -> `high64`. struct uint128 { uint64 low64 = 0; uint64 high64 = 0; uint128() = default; uint128(uint64 low64_, uint64 high64_) : low64(low64_), high64(high64_) {} friend auto operator<=>(const uint128 &, const uint128 &) = default; }; inline uint64 Uint128Low64(const uint128 & x) { return x.low64; } inline uint64 Uint128High64(const uint128 & x) { return x.high64; } // Hash function for a byte array. uint64 CityHash64(const char *buf, size_t len); // Hash function for a byte array. For convenience, a 64-bit seed is also // hashed into the result. uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed); // Hash function for a byte array. For convenience, two seeds are also // hashed into the result. uint64 CityHash64WithSeeds(const char *buf, size_t len, uint64 seed0, uint64 seed1); // Hash function for a byte array. uint128 CityHash128(const char *s, size_t len); // Hash function for a byte array. For convenience, a 128-bit seed is also // hashed into the result. uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed); // Hash 128 input bits down to 64 bits of output. // This is intended to be a reasonably good hash function. inline uint64 Hash128to64(const uint128& x) { // Murmur-inspired hashing. const uint64 kMul = 0x9ddfea08eb382d69ULL; uint64 a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul; a ^= (a >> 47); uint64 b = (Uint128High64(x) ^ a) * kMul; b ^= (b >> 47); b *= kMul; return b; } } #endif // CITY_HASH_H_